1. Field of the Invention
The present invention relates to a composition for the de-inking of printed waste paper by the "washing" process. The de-inking of printed waste paper is intended to remove printing ink from paper and to recover a paper pulp that may be used to prepare printing paper for newspapers, magazines, books, etc. The printing paper consists essentially of cellulose fibers and fillers, while the printing ink consists of pigments held together by suitable vehicles.
2. Description of the Prior Art
One of the best known de-inking processes is the so-called "washing" process. In this process, the printed waste paper is prepared in water and the resulting suspension is successively washed.
During pulping of the printed waste paper in water, the printed waste paper is crushed and fiberized in an alkaline medium, with the aid of heat, mechanical stirring, and suitable de-inking compositions which remove the ink more or less thoroughly from the paper fibers.
The washing involves a series of thickenings and dilutions of the aqueous solution obtained from the waste water pulping and is designed to result in the formation of two aqueous suspensions: a more dilute suspension containing the possibly greatest quantity of the ink, and a thicker suspension containing paper fibers that are as free as possible from the ink. This latter suspension is used in the manufacture of new paper.
In practice, in the known "washing" processes, the more dilute suspension containing the possibly greatest quantity of the ink contains a considerable amount of paper fibers and fillers, and the more dilute suspension must thus be suitably treated before being partially recycled or discharged as an effluent. In general, flocculants consisting of polyelectrolytes are added to the suspension which is then subjected to flotation in an acid or neutral medium. See U.S. Pat. No. 3,354,028 to Illingworth. Proceeding in this manner, however, the fibers and mineral fillers are floated together with the ink, thereby causing an important part of the fibers and the mineral fillers to be lost, which otherwise would be useful for the preparation of new paper.
Thus, and summing up, it may be said that with the de-inking compositions of the prior art and with the known de-inking "washing" processes the yield in recovered paper is in general relatively low. See Escher Wyss News, Vol. 44, 1971(1), pages 70 to 79.
Still another drawback of the known "washing" processes is that the floated mass, since it contains a considerable amount of fibers, has a considerable volume and, as such, is difficult to be disposed of.
Moreover, the clarified water obtained downstream of the flotation step may be recycled only in limited quantities to the pulping step and/or to the washing step, because of the considerable electrolyte content caused by pH corrections and flotation salt(s) addition. This causes the drawback of forcing the operator to dispose of large masses of water used in carrying out the overall process. Moreover, if it is desired to recycle part of the clarified acid water, it is necessary to correct the pH with the consequential consumption of reactants because in the pulping and washing steps one works in an alkaline medium.